The invention relates to a method for manufacturing a dental aspirator comprising an extruded plastic tube which forms a bellows portion spaced from the ends of the tube and limited to a minor portion of the tube length, said portion allowing angling of the tube and comprising a number of folds each of which consists of two cupshaped portions which have the concave surfaces facing each other and one of which has a smaller width than the other one in order to be snapped completely or partly into said other cupshaped portion when the plastic tube is bent in the bellows portion, for maintaining the bow produced.
A dental aspirator of this type is described in U.S. Pat. No. 4,417,874. It is not disclosed therein how such a dental aspirator shall be manufactured but it may be assumed that the manufacture takes place in the manner which is conventional as far as suction tubes are concerned intended for the intake of liquid and provided with a bellows portion so that the end of the suction tube which is inserted into the mouth can be angled in relation to the end which is immersed into the liquid. These suction tubes have a diameter of about 8 mm and have a relatively thin wall, which is a prerequisite for the bellows portion being produced since this portion according to the common method of manufacture which is described in U.S. Pat. No. 3,409,224, is formed by the tube wall in a special work operation which is separated from the extrusion and must be performed in a separate machine, is pressed and deformed against an inner mandrel by means of rollers engaging the outside surface of the tube. This method of manufacture is suitable only for tubes having a thin wall, i.e. tubes having a wall thickness up to some tenths of a millimeter. However, when dental aspirators are concerned this wall thickness is too small because a tube having such a thin wall will be easily flattened during shipping and handling particularly when it is to be connected to a suction hose or if the dentist when working in the oral cavity incidentally presses against the dental aspirator. Moreover, such a tube does not have the necessary stability in the bellows portion so that the dental aspirator after having been bent to the desired angle and suspended on the lower cheek, tends to be straightened out if tension occurs in the connected hose or even only by the weight thereof. There is accordingly a pronounced need of a more stable but nevertheless easily bendable dental aspirator of the kind referred to above, which can be manufactured in a rational and profitable manner, because it is a matter of maintaining a low price of these dental aspirators which are a one way product and thus are scrapped after each use.
The purpose of the present invention is to satisfy said need. The method of the invention is based on the method applied for a very long time according to U.S. Pat. No. 3,538,209 in connection with large diameter tubes for inter alia sewers but also according to U.S. Pat. No. 3,751,541 for common suction tubes, in connection with the extrusion of a tube having a smooth wall to impart to said wall a corrugated shape by forming the tube wall against endless chilled mold chains under the influence of pressure or vacuum, said chains being moved in an endless path at each side of the still soft and warm tube leaving the extruder. In this method the corrugation thus is effected continuously over the total length of the tube (U.S. Pat. No. 3,538,209) or over limited portions of the tube (U.S. Pat. No. 3,751,541) in direct connection with the extrusion of the tube. However, in that case a simple corrugation is concerned including annular bulges with substantially semicircular cross sectional shape.